Active hydrogen compounds aromatic nucleophilic substitution

Such results indicate that, from a mechanistic point of view, it is not a matter of a simple aromatic nucleophilic substitution (in any case very difficult if not yi benzyne), but more probably of a radical substitution on an activated complex of the TCDD (SRNl mechanism) (1 ) this mechanism is favoured by the fact that the radical anion of TCDD is particularly stabilized (IJ). How this radical anion is generated from the initiator peroxide and how it reacts with the hydrogen donor (PEG or the solvent) is not at this moment clear however, interesting to note, degradation of TCDD by u.v. irradiation leads to the same intermediate compounds. 

One significant difference between nitrocarboaromatics and aromatic azines is the tendency of the activating center of the latter to react with electrophiles or compounds capable of hydrogen bonding, thereby accelerating nucleophilic substitution. 

A variety of methods for the direct amination of nitrobenzene, that do not require halogenated aromatic compounds, have been reported, including both vicarious (eliminative) [16, 17,19,42] and oxidative versions of nucleophilic substitution of hydrogen. Recently, we have described the aminatimi of 1,3-dinitrobenzene promoted by fluoride ions through photochemical activation [43], Also, the use of KMn04 as oxidant is of great practical value [3,44]. 

The classical Vilsmeier-Haack reaction - involves electrophilic substitution of a suitable carbon nucleophile with a chloromethyleneiminium salt, for example salt (1). Suitable carbon nucleophiles are generally electron-rich aromatic compounds such as V,N-dimethylaniline (2), alkene derivatives such as styrene (3) or activated methyl or methylene compounds such as 2,4,6-trinitrotoluene (4 Scheme I). These compounds (2-4) react with salt (1) giving, after loss of hydrogen chloride, the corresponding im-inium salts (5-7). Hydrolysis of iminium salt (5) affords aldehyde derivative (8) and this transformation (Ar—H - Ar—CHO) is the well-known Vilsmeier-Haack formylation reaction. Hydrolysis of iminium... 

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